1. Field of the Invention
The present invention relates to an ink jet recording medium to which an aqueous ink is applied for carrying out recording. More particularly, it relates to a recording medium which is suitable for use to carry out color image recording thereon with an aqueous ink and which comprises a paper, a resin coated paper or a film as a support.
2. Related Art
The ink jet recording method performs recording of letters or images by allowing ink droplets ejected by various working principles on a recording medium. Ink jet printers have such favorable features that there is no limitation as to kind of recording patterns, that they can easily perform multi-color recording and that the maintenance thereof is easy. Therefore, the ink jet printers are rapidly becoming widespread as devices for producing hard copies of image information. The image information recorded on ink jet recording media which comprise a transparent film as a support is utilized as originals for presentation in conferences, lecture meetings, etc. by using overhead projectors together with photographic slides. Recording of image information by ink jet recording method for overhead projectors provides many merits.
As for the recording media used for ink jet recording, efforts have been made from the aspects of printer hardwares or ink composition in order to use woodfree papers or coated papers used for ordinary printing or writing. However, improvements in recording media have come to be required increasingly in order to go side by side with developments in printer hardwares such as ever increasing speed, development of ever finer definition and images of full color. That is, for recording media, it is required that image density of the printed ink dots be high and hue characteristics be bright and appealing, the ink absorbing capacity be great and the ink absorbing speed be high and as a result, the ink applied do not bleed or spread even though different color inks are put over additionally. Moreover, the circumference of dots should be sharp and demarcating. In order to meet these requirements, many proposals have been made. For example, Japanese Patent Kokai No.53-49113 discloses an ink jet recording sheet containing urea-formaldehyde resin powder and impregnated with a water-soluble polymer, but the ink jet recording sheets of this type suffer from the problems that the circumference of dots is apt to get blurred and besides, density of dots is low.
Further, Japanese Patent Kokai No.55-5830 discloses an ink jet recording sheet comprising a support and an ink absorbing coating layer provided thereon; Japanese Patent Kokai No.55-51583 discloses to use an amorphous silica powder as a pigment in the coating layer; and Japanese Patent Kokai Nos.59-174381, 60-44389, 60-132785 and 60-171143 disclose ink jet recording sheets which have a transparent ink-receiving layer. These ink jet recording media of coated paper type are improved over the ink jet recording sheets of plain paper type in dot diameter, shape of dots and image density, but are still insufficient in the ink absorbing speed. Especially, when dots of a plurality of aqueous inks overlap in multi-color recording, there sometimes occur the problems that the inks spread or the inks transfer to the guide roll of printing devices owing to insufficient drying of inks or insufficient absorption of inks to cause staining of the recorded images.
On the other hand, as to the ink jet recording media comprising a transparent support on which image information used for overhead projectors is recorded, ink absorbing inorganic pigment cannot be used in a large amount because use of the pigment generally damages transparency and in many cases, the ink absorbability depends on the properties of the resin layer formed on the surface of the transparent support. Examples of the resins conventionally used for this purpose are polyvinyl pyrrolidone and polyvinyl pyrrolidone-vinyl acetate copolymer disclosed in Japanese Patent Kokai No. 57-38185, copolymers of polyvinyl alcohol and olefins or styrene and maleic anhydride disclosed in Japanese Patent Kokai No. 60-234879, crosslinking products of polyethylene oxide and isocyanate compounds disclosed in Japanese Patent Kokai No.61-74879, blends of carboxymethyl cellulose and polyethylene oxide disclosed in Japanese Patent Kokai No.61-181679, and grafted polymers of methacrylamide on polyvinyl alcohol disclosed in Japanese Patent Kokai No.61-132377.
In all of the above methods, when a number of ink dots are printed on the surface of a recording medium at a high speed as in the case of high speed multi-color recording, the ink absorbing speed and the ink absorbing capacity are both insufficient and there are serious problems on quality of recorded images such as spread of dots, unevenness in color or density caused by blending of inks between adjacent dots and unevenness in solid print portions. Furthermore, since the recorded image is insufficient in water resistance, there are another problems that the ink dye bleeds due to deposition of waterdrops and the surface of the recording medium is dissolved with water.